Rare‐Earth Doped Hydroxyapatite Nanoparticles for Biomedical Applications: A Comprehensive Review From Bone Regeneration to Cancer Theranostics

Rare‐earth element (REE)‐doped hydroxyapatite nanoparticles (HAp‐NPs) have emerged as multifunctional bioceramics with significant potential across diverse biomedical fields, owing to their excellent biocompatibility, bioactivity, and tunable physicochemical properties. Recent advances in the doping of HAp‐NPs with lanthanide ions have expanded their functionality, enabling innovative applications in bone tissue engineering, targeted drug delivery, cancer therapy, dentistry, and biomedical imaging. This review provides a comprehensive assessment of the synthesis strategies and surface modification techniques, utilizing both natural and synthetic precursors, for REE‐doped HAp‐NPs. Particular attention is given to the role of individual REE dopants (e.g., La 3+ , Ce 3+ , Pr 3+ , Eu 3+ , Gd 3+ , Er 3+ , Sm 3+ , Nd 3+ , Dy 3+ , Tb 3+ , Yb 3+ , and Y 3+ ) in modulating the luminescent, antibacterial, osteoconductive, and drug‐delivery properties of HAp‐NPs. Furthermore, the theranostic potential of these nanomaterials is examined, emphasizing their low cytotoxicity, high loading capacity, efficient cellular uptake, and advanced imaging capabilities. Collectively, REE‐doped HAp‐NPs represent a versatile and promising platform for the development of next‐generation nanomedicines, with broad implications for precision therapy and regenerative medicine.